Can't install any extension, and can't access my drive on chromebook

Hello, Linux environment is running on my chromebook, thunderbird has been installed. 2 issues: - When I try to install an extension, I always get a message "This extension will have permission to have unlimited access to thunderbird and the computer". and I'm stuck. The add button does not trigger any action. This does the same thing if I want to install a dictionary from the settings. - I have no access shared folders like my Drive on my Chromebook, despite having Linux sharing enabled. Thank you for your help Céline